This disclosure relates generally to optoelectronic devices and more particularly to a light emitting device having two or more light emitting diodes (LEDs), a planarized layer, a continuous wavelength conversion member and a light shaper. This disclosure also relates to a method for fabricating the light emitting device.
Light emitting devices containing light emitting diodes (LEDs) have been developed that are interchangeable with conventional light bulbs having incandescent and fluorescent light sources in lighting systems. In various applications, light emitting devices can include two or more light emitting diodes (LEDs) on a circuitry substrate configured to form a light beam. One shortcoming of this type of light emitting device is that the light beam can have a non uniform light intensity and color across its width.
Referring to FIG. 1, a prior art light emitting device 10A includes a circuitry substrate 12A and four spaced light emitting diodes (LEDs) 14A in a spaced array. Each light emitting diode (LED) 14A includes a separate wavelength conversion member. This configuration produces a discontinuous light intensity and light output. As shown in FIG. 2, the light emitting device 10A produces a luminance pattern 16A comprised of the individual light outputs of the light emitting diodes (LEDs) 14A and individual wavelength conversion members, with the highest light outputs of the light emitting diodes (LEDs) 14A represented by the four peaks. As also shown in FIG. 2, due to the spacing of the light emitting diodes (LEDs) 14A and discontinuous wavelength conversion members, there are gaps in the light density of the luminance pattern 16A. These gaps form undesirable shadows in the application side. For example, in an automotive head lighting system, the gaps can form dark spots during operation of a vehicle at night.
Referring to FIG. 3, a prior art of light emitting device 10B includes a circuitry substrate 12B and four light emitting diodes (LEDs) 14B mounted to the circuitry substrate 12B. In addition, electrical connection wires 17B, which are encapsulated in an optional wire protection material 18B, electrically connect the light emitting diodes (LEDs) 14B to electrodes on the circuitry substrate 12B. Each light emitting diode (LED) 14B includes a separate wavelength conversion member 15B, which are discontinuous and spaced from one another. The discontinuous wavelength conversion members 15B along with the wire protection material 18B form dark areas DA and bright areas BA, and a non-uniform brightness and color across the emitting surface of the light emitting device 10B. One shortcoming of this type of light emitting device 10B is that resultant light beam can also have a non uniform light intensity across its surface area.
Referring to FIG. 4, another prior art light emitting device 10C includes a circuitry substrate 12C and four light emitting diodes (LEDs) 14C mounted to the circuitry substrate 12C using wires 17C and an optional wire protection material 18C as previously described. The light emitting device 10C also includes wavelength conversion members 15C formed on light emitting diodes (LEDs) 14C using a phosphor spray coating process. As with the previous light emitting device 10B, the wavelength conversion members 15C have non-uniform thicknesses, and non planar surfaces across the surface area of the light emitting device 10C. Again this configuration can produce a non uniform light intensity as well as dark areas and bright areas.
Referring to FIG. 5, another prior art light emitting device 10D includes a circuitry substrate 12D and four flip chip light emitting diodes (LEDs) 14D bonded to the circuitry substrate 12D. Each flip chip light emitting diode (LED) 14D includes a p-electrode and an n-electrode bonded to corresponding electrodes on the circuitry substrate 12D. The light emitting device 10D also includes a wavelength conversion member 15D enclosed by a dam 13D both of which are formed using a dispensing process. In this type of light emitting device 10D large color differences can occur due to side emitting and center emitting from the light emitting diodes (LEDs) 14D. For example, the path of a side light beam S passing though the wavelength conversion member 15D is longer than the path of a center light beam C. In the side light beam S more photons are converted by the wavelength conversion member 15D producing color differences relative to the center light beam C, such as yellowish side emitting or color shifting side emitting. This configuration does not produce an ideal color uniformity. In addition, the wavelength conversion member 15D, which is formed using a dispensing process, typically has a non-uniform thickness and planarity, which also contributes to non-uniformity in brightness and color.
Referring to FIG. 6, another prior art light emitting device 10E includes a circuitry substrate 12E and four flip chip light emitting diodes (LEDs) 14E bonded to the circuitry substrate 12E. The light emitting device 10E also includes a wavelength conversion member 15E formed on the light emitting diodes (LEDs) 14E using a phosphor spray coating process. In this embodiment, there are gaps between the light emitting diodes 14E, which are filled by a protection or reflection material 11E to reduce the color shifting from side emitting. However, the intensity brightness cannot be uniform due to light blocking by the protection or reflection material 11E.
Referring to FIG. 7, another prior art light emitting device 10F includes a circuitry substrate 12F and four white light emitting diodes (LEDs) 14F bonded to the circuitry substrate 12F. Each light emitting diode (LED) 14F includes a p electrode, an n electrode, a side wall w, and wavelength conversion member 15F. There are the gaps between the white light emitting diodes (LEDs) 14F and a light beam produced by the light emitting device 10F can have a non uniform light intensity and color across its width.
In view of the foregoing, there is a need in the art for a light emitting device that produces a light beam having a uniform color and light intensity across its width. The present disclosure is directed to a light emitting device having a uniform brightness and definition and to a method for fabricating the light emitting device.